Get Fuzzy on the Extinction of the Dinosaurs

Last Monday's 'Get Fuzzy' strip featuring Satchel the dog and Bucky the cat. By Darby Conley

What killed off the non-avian dinosaurs? Over the years climate change, mammals with a taste for dinosaur eggs, the laziness of dinosaurs, and even hungry, hungry caterpillars have been blamed, with the current favored culprit being an asteroid that struck in the vicinity of today’s Yucatan peninsula about 65 million years ago. But Bucky the cat from the comic strip Get Fuzzy isn’t convinced that scientists are any closer to solving the mystery.

In a string of strips that started on September 20, Bucky goes off on a tear about science when Satchel tells him that dinosaurs were killed by “a rare kind of flying rock” (which Bucky misinterprets as a “space hemorrhoid”). From there Bucky’s idle speculations begin to spin a little out of control—I won’t spoil it for you; go read the strips—but I think Bucky’s wild ideas underscore an important lesson. While it was controversial three decades ago, today we take the idea that the end-Cretaceous extinction was caused by an asteroid for granted. Many books and documentaries refer to it, but relatively little detail is ever given about the ecological crisis it caused or how the impact could have killed so many forms of life. (And, of course, there are still some who argue that the impact would have been insufficient and that intense volcanic eruptions or some other cause triggered the extinction.) If we really want to inform the public about science, just saying a flying rock did it doesn’t cut it.

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Stegosaurus Week: The Weak Bite of Stegosaurus

An Allosaurus menaces a Stegosaurus and its offspring. Image from Wikipedia.

In discussions of dinosaur bite mechanics, the heavy forces generated by predatory species often dominate, but it is important to understand how the jaws of herbivores worked, too. The jaws of Stegosaurus might not be as immediately impressive as those of Tyrannosaurus rex, but it is still important to know how they were put to use if we are to understand the paleobiology of the famous armored dinosaur. Now, thanks to computer models created by Miriam Reichel, we can better understand what Stegosaurus was capable of eating.

The teeth of Stegosaurus are almost all the same: a series of rounded, minutely-ridged teeth arranged in straight rows from front to back. To investigate how this dental arrangement would have worked while consuming food, Reichel created 3-D models of the teeth (both with ridges and without) to create a virtual model of Stegosaurus jaws. This digital dinosaur was then set to work on computer-generated cylinders given the properties of different types of plant food, using the muscle attachments seen on the dinosaur’s skull to determine how hard its bite would have been.

As calculated by Reichel, Stegosaurus didn’t have a very powerful bite. Even you and I could bite harder than Stegosaurus. The dinosaur could generate enough force to crunch through twigs and branches under a half an inch in diameter, but anything bigger than that and it would have a difficult time of it. Given its weak jaws, Stegosaurus would have had to rely on soft, fast-growing plants; it is fantastic to think that this large dinosaur could have survived on such a diet!

Then there is the matter of the actual method by which Stegosaurus processed its food. It probably did not chew its food to any great degree, but instead sliced through soft plants before swallowing. Additionally, Reichel proposes that Stegosaurus may have had a tough beak at the front of its jaws which took most of the punishment during feeding. The teeth were left with the lighter work, although, since Stegosaurus jaws were weakest at the front, this might mean that it was only eating the softest, greenest food available. Further study will be required to understand the precise mechanics of how Stegosaurus ate, but, at the very least, Reichel’s work confirms that this dinosaur had to carefully pick out soft Jurassic salads for lunch.

Reichel, M. (2010). A model for the bite mechanics in the herbivorous dinosaur Stegosaurus (Ornithischia, Stegosauridae) Swiss Journal of Geosciences DOI: 10.1007/s00015-010-0025-1

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New Horned Dinosaurs From America’s Lost Continent

Skeletal restorations of Utahceratops (left) and Kosmoceratops (right). The yellow bones are those that have been recovered for each species. From Sampson et al., 2010.

At the height of the golden era of dinosaur science, it takes something special for a newly described dinosaur species to stand out. Dinosaurs with dual sickle claws, humps,  or unexpected bristles more readily grab the attention of the public than more familiar-looking forms, but looks aren’t everything. A pair of horned dinosaurs described today in PLoS One are noteworthy for reasons that go beyond their strange appearances.

A few months ago, I was fortunate enough to visit the Utah Museum of Natural History’s paleontology field crew at their camp in southern Utah’s Grand Staircase-Escalante National Monument. The arid, rocky landscape was rich in dinosaur fossils, but 75 million years ago this same place would have looked very different. During that time in earth’s history, near the close of the Cretaceous, a shallow sea over the center of North America divided the landmass into two separate continents: Appalachia to the east and Laramidia to the west. The area which is today Grand Staircase-Escalante National Monument was in the middle of the thin western continent, and according to Scott Sampson, University of Utah paleontologist and lead author of the new paper, the place was “a wet, swampy setting akin to present-day northern Louisiana.” Crocodiles, turtles, and at least 16 unique species of dinosaurs thrived here, including the two horned dinosaurs announced today.

Named Utahceratops gettyi and Kosmoceratops richardsoni, respectively, the two dinosaurs belonged to a subdivision of the horned dinosaur family called chasmosaurines. Roughly speaking, this group of horned dinosaurs can often be identified by their large brow horns and their wide, squared-off frills, and both Utahceratops and Kosmoceratops fit the classic chasmosaurine type. Nevertheless, both were distinct from species previously recognized and were significantly different from each other. While Utahceratops had relatively short brow horns in front of a large frill that was slightly indented inwards along its top margin, the slightly smaller Kosmoceratops had longer brown horns and an array of spikes that spilled forwards over its frill like a chasmosaurine comb-over.

In contrast to more familiar chasmosaurines like Triceratops, though, the browhorns in both Utahceratops and Kosmoceratops were oriented out to the side rather than forward. Why this should be so is unclear. Co-author Andrew Farke of the Raymond M. Alf Museum of Paleontology says, “it’s hard to know for sure, but in modern horned animals horn orientation usually relates to horn function.” Perhaps Utahceratops and Kosmoceratops had similar styles of combat with members of their own species, Farke hypothesizes, or maybe the peculiarity was inherited in both from a common ancestor. Likewise, according to Sampson, the sideways orientation of these horns is also seen in another horned dinosaur from Coahuila, Mexico, and may be a common characteristic of chasmosaurines from this part of Laramidia. Among these dinosaurs, “the sideways-oriented horns offer another means to lock heads and engage in contests of dominance,” Sampson says; “they would also have made effective visual signals, particularly in Kosmoceratops.”

Utahceratops and Kosmoceratops were also very different from the horned dinosaurs that lived in the same area a few million years earlier. While both of the new dinosaurs came from the Kaiparowits Formation, horned dinosaurs of a different sort have been found in the national monument’s 80-million-year-old Wahweap Formation. These older dinosaurs, such as the many-horned Diabloceratops, belonged to another branch of the horned dinosaur family tree called the centrosaurines. “If you were to line up the skulls [of the Wahweap and Kaiparowits dinosaurs] side by side,” Farke says, “they would look strikingly different!” especially since the two newly described dinosaurs had relatively larger and more ornamented frills.

Given the degree of completeness of both dinosaurs (entire skulls for both, the majority of the skeleton of Utahceratops, and the skeleton except the tail, feet, and forelimbs in Kosmoceratops), their description is a major contribution to our understanding of ceratopsid anatomy and diversity. What makes them especially noteworthy, however, is that they confirm the existence of disparate pockets of dinosaur evolution along the western continent of Laramidia. These genera were not evenly spread from Mexico to Canada, but were distinct from the horned dinosaurs that lived at the same time in the northern part of the continent. This is not just an accident of sampling, the authors of the new study propose, but a signal of a real biogeographical phenomenon.

The picture that emerges from the distribution of the horned dinosaurs around 75 million years ago is that there were at least two separate centers of chasmosaurine evolution on the western continent. Where there were Chasmosaurus, the recently-described Mojoceratops and Vagaceratops (previously Chasmosaurus irvinensis, but renamed by the authors of this study) to the north, Utahceratops, Kosmoceratops and Pentaceratops lived in the far south. Based on the distribution of these dinosaurs in space and time, Sampson, Farke and their colleagues propose that about 77 million years ago there was a barrier that separated chasmosaurines in the north from those in the south. This barrier would have precipitated the divergent evolution of the northern and southern groups identified in the study, though the close relationship of Kosmoceratops and Vagaceratops found by the scientists suggests that these dinosaurs shared a close common ancestor that spread after this impediment was removed about 75.7 million years ago. As Sampson states by e-mail, the recognition of this patten raises some important questions about dinosaur evolution on Laramidia:

The implications of this finding huge, given that Laramidia was a landmass about one-third the size of present day North America, and much of this area was likely off limits to large dinosaurs because of large mountain ranges to the west.  Today we have a handful of rhino-to-elephant sized mammals living on Africa.  At present, it seems that there were at least 15-20 rhino-to-elephant sized animals living on Laramidia 76 million years ago, despite the fact that it was less than one-fifth the size of Africa.  How did so many species of giants co-exist on such a small chunk of land?  The answer may relate to available fodder (more biomass than at present) and/or to metabolic rates (slower in dinosaurs than in mammals).  Either way, these finding suggest that the hothouse world of dinosaurs was, at least in some respects, very different than the one we know today.

Furthermore, if the pattern of evolution in these horned dinosaurs really was influenced by the existence of an ancient barrier, then the same signs of isolation should be seen among other dinosaurs, as well. Hadrosaurs and tyrannosaurs probably would have been isolated in the same way, and the discovery and description of additional dinosaurs from Grand Staircase-Escalante National Monument will be pivotal in further tests of this idea. Determining just what the barrier might have been, though, is another mystery. At present there is no sign of an actual physical barrier, though the authors of the new study suggest a previously-unidentified mountain range, temporary flooding by the nearby sea, a turbulent river system, or some kind of ecological barrier as possibilities.

The story of Laramidia will not be resolved by one paper alone, but will take years of study by many paleontologists. This is a good thing. Through something as simple as the description of two dinosaurs, paleontologists have placed the fauna of an entire lost continent in a new context, and, armed with a new set of questions, paleontologists can return to the strata of southern Utah in search of answers.

References:

Sampson, S., Loewen, M., Farke, A., Roberts, E., Forster, C., Smith, J., & Titus, A. (2010). New Horned Dinosaurs from Utah Provide Evidence for Intracontinental Dinosaur Endemism PLoS ONE, 5 (9) DOI: 10.1371/journal.pone.0012292

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Dinosaur Drive-In: When Dinosaurs Ruled the Earth

If paleontologists have said it once, they have said it a hundred times: non-avian dinosaurs and humans never coexisted. Most people who insist otherwise are creationist cranks who believe that evidence of a living dinosaur would somehow undermine evolutionary theory, but I understand that Hollywood has to play by different rules. Dinosaurs are just not as exciting without people to menace, and so it has been traditional to use time travel, the existence of prehistoric “lost worlds,” fertilized eggs preserved for over 65 million years and genetic engineering experiments gone awry to bring dinosaurs and people together. But none of these options worked for the creators of the 1970 Hammer film When Dinosaurs Ruled the Earth. They wanted dinosaurs and other prehistoric monsters to attack scantily-clad cavepeople, and so they made a film that a biblical fundamentalist could take as a documentary rather than fiction.

When Dinosaurs Ruled the Earth doesn’t begin with a shot of a steaming, primeval forest, but of a gaggle of tanned and oiled cavepeople who have crawled out of their cliffside dwellings to engage in their regular “let’s pick which blond woman we want to sacrifice” ritual. Naturally, the prospective victims are not very happy about this—one throws herself off a cliff—but when they try to escape they are hindered by the fact that they are wearing prehistoric underwear so skimpy that it actually makes it more difficult for them to run away. It would have made more sense for them to lose the push-up bras and just bolt for it, though I imagine going streaking during prehistory would have presented its own unique risks.

In any event, one of the Cenozoic supermodels—named Sanna—does manage to escape by jumping into the sea and is promptly rescued by a conveniently placed group of fishermen whose unfortunate garments remind us why it’s never wise to wear thongs in a windstorm (I wish I were talking about sandals here—yikes). It is among this group of unfortunately attired men that we meet Tara, our film’s scruffy male lead. Meanwhile, back at the ranch, the musclebound leader of the cavepeople is clearly upset that the sacrifice did not go as planned; he shouts incomprehensible phrases and gestures widely to get people to go do whatever it is they do. Maybe this was intended as a bit of fun for the audience—make up your own dialogue as you go along—especially since words like “akita” appear to mean: “Over there”; “Stop”; “Give me that”; “Come over here” and “Let’s have pancakes for dinner tonight.”

For me, though, the film’s real stars are the prehistoric creatures that help to thin out the cast, and the audience’s first look at one of the film’s exquisite stop-motion monsters comes when the fishermen return with the woman to their camp. While the dudes were out fishing, someone brought a plesiosaur (which is, of course, not a dinosaur) to the big clam bake, but damned if they knew what to do with the thing. It was too angry to just stick an apple in its mouth and start slow-roasting it, and when half the village runs over to examine their new visitor their dinner tries to make a break for it. Unfortunately, though, the plesiosaur wanders right into a mess of fluid the tribe uses for lighting fires, and soon the only question on anyone’s mind is: “White meat or dark?”

Things don’t look so rosy the next day. The cliffdwellers are still miffed that their sacrifice just up and left, and Tara’s wife isn’t too happy that he came back with a new, blond girlfriend. When Sanna’s captors show up, she makes a break for it, and thanks to an assist from an angry Chasmosaurus she gets a little extra time to get away. That does little to help the fisherman and his friends, though—when they set out after her the same dinosaur causes them a spot of trouble before throwing itself into what sounds like a bottomless pit (lots of roaring, but no crash). Sanna also encounters some of the dangerous local fauna when she finds herself being enveloped by a carnivorous plant, although I would not recommend her escape technique of reaching outside to stab inwards at the plant’s tough outer hide (pointsy towardsies = bad).

The remainder of the film is little more than an excuse to watch Victoria Vetri run around in an embarrassingly small bikini. Thankfully, there are a few more prehistoric critters to help break the movie’s naked tedium. A newly-hatched baby something-o-saurus and its mother (which look like cousins of the Beast from 20,000 Fathoms) provide a brief bit of comic relief as they try to figure out whether Sanna is friend or food; an attack by an oversized Rhamphorhynchus livens things up a bit, and when Tara returns home to find that his tribe doesn’t think it’s cool that he ran off with someone else’s sacrifice, they try to serve him up on a raft to the local Tylosaurus. (The marine reptile responds by tossing him off the raft. “Yecch! Human? No thanks – I’m trying to cut back on junk food.”) Given how good these stop-motion creatures look, though, it is sad that the film also resorts to gluing plates and spikes on alligators and monitor lizards and making them fight, a practice that is despicable as it is lazy.

In the end, a giant tidal wave wipes away the coastal village but delivers our heroes to a mountaintop to observe a lunar eclipse. Dumb, but attractive, they would go on to found a settlement along the southern coast of California which would eventually be named Los Angeles. What happened to all the prehistoric monsters is unclear, though. Perhaps they got so tired of the cavepeople’s shenanigans that they eventually died of boredom—a risk I certainly felt while watching this vintage 1970s schlock.

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Stegosaurus Week: Tracking Cryptic Stegosaurs

The partial skeleton of Dacentrurus described by Richard Owen. From Wikipedia.

The first trace of the plated, spiky stegosaurian dinosaurs was found in Early Cretaceous rock near Grahamstown, South Africa. Uncovered by W. G. Atherstone and A. G. Bain in 1845, the dinosaur was represented by a partial skull and several limb bones. The naturalists felt unqualified to study them and sent the fossils to Richard Owen in England. When Owen eventually got around to describing them, he confused parts of the stegosaur with bones from armored reptiles called pariesaurs which came from South African rock of much older age. Things only got worse from there.

In 1890 the naturalist Richard Lydekker realized that Owen had erred, and he instead attributed all the material to a pariesaur, but Lydekker was wrong, too. When the paleontologist Robert Broom looked at the same material in 1910, he saw that some parts definitely belonged to a dinosaur, which he thought was an ankylosaur. Franz Nopcsa disagreed, casting the fossils as belonging to a stegosaur in his own 1929 study, but it was not until 1981 that paleontologists P.M. Galton and W.P. Coombs straightened things out. The dinosaur was indeed a stegosaur, and is called Paranthodon africanus today.

Paranthodon was not the only cryptic stegosaur with a tortured history. As reviewed by Susannah Maidment in her new paper on the history of stegosaur discoveries, in 1874, just three years prior to the description of the famous Stegosaurus, the scrappy remains of another stegosaur were found in Bedfordshire, England. Described as a partial skull by H.G. Seeley—though actually part of a vertebra—Craterosaurus pottonensis was so incomplete that it was not recognized for what it was until the 1980s.

Another stegosaur, called Omosaurus armatus by Richard Owen (and known as Dacentrurus today), was found the same year in Swindon, England, though its discovery, too, was plagued by confusion over whether its armored plates belonged to the dinosaur or were the head plates of a giant fish. We can look back at them today as the first stegosaurs to be described, although the fossils that initially set the image of what this group was like were the specimens found by O.C. Marsh and E.D. Cope during the “Bone Wars” of the late 19th century.

We have come a long way since Craterosaurus, “Omosaurus,” and Stegosaurus were initially described. Since that time stegosaurs have been found in the Middle Jurassic to Early Cretaceous rock of North America, Europe, Africa and Asia, although the most familiar one is perhaps one of the strangest. Stegosaurus lacked the large shoulder spikes seen among other dinosaurs of its kind, and it had an alternating pattern of plates on its back rather than a combination of back spikes and plates arranged in straight double rows. Even compared to other groups of dinosaurs, though, the stegosaurs were among the most unusual groups of dinosaurs to have ever lived, and new discoveries—such as species with extra-long necks—continue to underscore how bizarre they were.

References:

Maidment, S. (2010). Stegosauria: a historical review of the body fossil record and phylogenetic relationships Swiss Journal of Geosciences DOI: 10.1007/s00015-010-0023-3

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Dinosaur Sighting: A High-Class Triceratops

A metallic Triceratops, photographed on the grounds of a Minneapolis mansion. Photo by Mark Ryan.

I never would have thought of Minnesota as a hot spot for dinosaurs, but reader Mark Ryan keeps sending in sightings from the Gopher State. His latest submission is of one of several metallic dinosaurs that once graced the lawn of a mansion in uptown Minneapolis. The question is, what dinosaur was it? It clearly had the elongated frill and brow horns of what has previously been called Torosaurus, but the solid frill is a dead giveaway for Triceratops. Given the new debate over whether “Torosaurus” is really just an adult Triceratops, perhaps this sculpture can be seen as a sort of transitional growth phase, though—since it was built many years ago and has recently disappeared from the lawn—I wouldn’t bet on it.

Have you stumbled across a dinosaur in an unexpected place? If you have, and have a photo of the encounter, send it to us via dinosaursightings@gmail.com!

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The Many Layers of Cretaceous China

In order to understand the ecology of any environment, past or present, you must be able to change the scale of your perspective. Large animals are readily apparent, but what about the interactions between the plants they eat, the insects on those plants, the pollen on those insects, the many microorganisms in the habitat and so on? It is practically impossible to keep all these parts of an ecosystem in mind at once, but if we alter the scale of our perspective, we can better appreciate a greater array of interactions that might otherwise go unnoticed.

Artist John Conway has just created a stunning example of the nested levels of interactions between organisms in a new video. The scene is of prehistoric China’s famous 133-million to 120-million-year-old Jehol biota. At first only the dinosaur Jinzhousaurus and a pair of the pterosaur Jeholopterus can be easily seen, but as the camera zooms in the wasp Tanychora beipioensis comes into view, and it is covered with the pollen grains Protoconiferous funarius. The painting is an amazing reminder that there was much more to prehistoric ecosystems than dinosaurs and the plants they ate, but how did Conway create it? In an interview with paleontologist David Hone on the Archosaur Musings blog, Conway briefly explained the method and motivation behind the piece:

It’s a series of paintings done in Photoshop at successively smaller scales, then stitched together and animated in After Effects.

I was looking for a way to get across the sheer breadth of scale in the fossil record, from dinosaurs to pollen in this case. I was also looking for a way to make picture of a biota without having to do a “menagerie” painting, which is otherwise a necessary evil if you want to get a lot of animals in the one scene.

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Stegosaurus Week: Playing the Stegosaur Name Game

A reconstruction of Hesperosaurus on display at the Museum of Ancient Life at Thanksgiving Point, Utah.

Measuring diversity in the fossil record can be a tricky task. Short of inventing time travel, there will be always be some uncertainty about how many species of dinosaur existed at any one place and time, and as we learn more about the fossil record it may turn out that what we once thought to be distinct species or genera really belonged to already-known taxa (or vice versa). Stegosaurs are not immune from such lumping and splitting, and in his contribution to the stegosaur issue of the Swiss Journal of Geosciences, paleontologist Ken Carpenter used the debate over Hesperosaurus to dig into what distinguished this armored dinosaur from Stegosaurus.

Earlier this week I wrote about a new study describing skin impressions and other soft-tissue traces of the stegosaur Hesperosaurus mjosi. What I did not mention was that some paleontologists have proposed that this dinosaur was actually a smaller species of the more famous Stegosaurus genus, which would make its name Stegosaurus mjosi. Carpenter, who was one of the scientists who named Hesperosaurus in 2001, disputes this, but notes that whether the contentious stegosaur falls into one group or the other relies on more than anatomy alone.

Back in the Bone Wars era, when Stegosaurus was first described, paleontological rivals E.D. Cope and O.C. Marsh were in uncharted territory as far as taxonomy was concerned. The bits and pieces of the fossil animals they found had not been seen before, so it is not surprising that they created a vast accumulation of names to label them all (to say nothing of the competition between them that likely influenced their scientific practices). Given what we know now, though, any paleontologist who applied a new name to every bone scrap they found would be derided by the paleontological community. The naming of a new species—or the synonymy of two old ones—must be explained in minute detail, but even then different scientists have different perspectives on how different two fossils have to be in order to be designated as two different species.

That different species of dinosaur actually existed is immediately obvious. Tyrannosaurus rex and Stegosaurus stenops were so different from each other that it is at once apparent that they were two distinct species of dinosaur. Where a scientist’s personal views come into play are cases where there are two groups of animals which are only slightly different from each other. Do these two groups represent different growth stages of the same animal, different populations of the same species, different species of the same genus, or well-distinguished genera which can readily be told apart? Since, as Carpenter notes, dinosaur taxonomy is based on the comparison of bones alone, disputes can easily arise over how much variation a species had and what falls outside that range.

As for Hesperosaurus, the debate over its validity has been greatly influenced by the material O.C. Marsh used to create the name Stegosaurus armatus in 1877. The fossils were very scrappy, and compared to skeletons discovered since the 19th century, are not very useful in distinguishing these bones from other better-established Stegosaurus species such as S. stenops and S. ungulatus. This means that almost any restoration of the first species Marsh described, Stegosaurus armatus, is going to be a composite of other specimens and therefore obscure the defining characteristics of Stegosaurus as seen in the other species. As a result, it would be possible to lump almost any dinosaur with characteristics similar to the sparse materials Marsh found into the genus Stegosaurus, and it was on that basis that Hesperosaurus was proposed to be a unique species of Stegosaurus.

As Carpenter (and, in the same volume, Peter Galton) argues, however, Stegosaurus armatus is not the best dinosaur to use for determining differences between Stegosaurus species. If the more complete Stegosaurus stenops is taken as representative of the genus, it clearly differs in enough characteristics from Hesperosaurus for both to be considered separate genera. In fact, the differences between them have only become more apparent since more complete specimens of Hesperosaurus have become known.

Overall, I think Carpenter makes a solid case for Hesperosaurus; when compared to the better-known species of Stegosaurus, it was clearly a very different animal. Nevertheless, the fact that two groups of animals were easily distinguishable from each other does not tell us whether we should group them as different species or genera. That is something that is proposed, debated and revised according to the ideas of scientists, and there is no doubt that paleontologists will continue to play the dinosaur name game as research continues.

References:

Carpenter, K. (2010). Species concept in North American stegosaurs Swiss Journal of Geosciences, 103 (2), 155-162 DOI: 10.1007/s00015-010-0020-6

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A Strange Sail-Backed, Bristly-Armed Dinosaur

A life restoration of Concavenator by artist Raul Martin. From Ortega et al., 2010.

When I logged on to Facebook Wednesday morning, one of the first things I saw was a cryptic status update from University of Maryland paleontologist Thomas Holtz. He speculated that the paleo community at large would be “duly impressed” by something set to debut later in the day, but what was it? I jokingly replied that it would have to be something pretty impressive to outshine the weird raptor Balaur bondoc, but Holtz was right. Described in this week’s issue of Nature, Concavenator corcovatus is one of the strangest dinosaurs ever found, and possibly one of the most significant.

On a superficial level, Concavenator looks very familiar. Discovered in the approximately 130-million-year-old rock of Spain, this dinosaur was a carcharodontosaurid, or an early relative of the giant Giganotosaurus and a somewhat distant cousin of Allosaurus. What made it unique, however, were a series of elongated, upward-pointing neural spines near its hips. This dinosaur did not have a sail running the length of its back, like Spinosaurus, nor did it have a more uniform set of elongated neural spines, like the carcharodontosauid Acrocanthosaurus, but instead had two neural spines that jutted up high right in front of its hips followed by a series of shorter—but still elongated—spines at the base of its tail. This kind of arrangement—a short, tall sail near the hips—had been proposed for a very incompletely known dinosaur named Becklespinax before, but with the mostly complete remains of Concavenator we now know that at least some predatory dinosaurs had this weird decorative arrangement.

With two (and possibly three, if Becklespinax turns out to belong to the same group) carcharodontosaurids with strange structures on their backs, sails, humps, or fins may very well be found on other members of this group. But, despite its flashy sail, the most impressive aspect of Concavenator is much more subtle. Arrayed in a line along its ulna—one of the two bones that make up the forearm—were a series of round, raised bumps. This is not the first time paleontologists have seen such a feature. In 2007 it was announced that Velociraptor had these same structures, and they looked identical to the quill knobs on the arms of birds where arm feathers attached. The question was: what was a dinosaur so far removed from the origin of birds doing with quill knobs?

During the past two decades, a flood of new fossils has confirmed that birds evolved from one lineage within the diverse, feather-covered group of theropod dinosaurs called coelurosaurs. Almost every lineage within this group has at least one feathered representative, but Concavenator was not a coelurosaur. As a carcharodontosaurid, its lineage last shared a common ancestor with the coelurosaurs back in the Middle Jurassic, and the knobs on its arms represent the first evidence of a body covering other than scales on a theropod outside the coelurosaurs. Just what these knobs supported is as yet unknown. Perhaps they were feathers, or maybe they were a kind of bristle that was structurally similar to feathers. Skin impressions from other parts of the dinosaur show that it was not entirely covered by such structures, meaning that Concavenator may have had a mosaic of scales and feather-like structures on its body.

Even better, the discovery that Concavenator had a type of filamentous body covering reinforces the emerging hypothesis that dinosaurs as a whole may have sported a variety of such structures. Within the past decade paleontologists have found at least two examples of ornithischian dinosaurs (Psittacosaurus and Tianyulong) with feather-like bristles on their backs. These animals were all the way on the other side of the major evolutionary divide in the dinosaur family tree—about as distantly related to birds as possible while still being dinosaurs—yet they, too, had unique body coverings that were similar in structure to the fuzzy precursors of feathers seen in some coelurosaurs. If ornithischians had bristles, coelurosaurs had feathers, and carcharodontosaurids had similar structures, then it is possible that feather-like body coverings were a common trait for dinosaurs that might go all the way back to their origins. Either that, or these structures independently evolved in different lineages multiple times during evolutionary history. Regardless of which hypothesis turns out to be correct, we need to rethink what we thought dinosaurs looked like, and I expect that we are going to see the discovery of further evidence in the years to come that many dinosaurs were feathery, bristly creatures.

Post-script: There is some debate as to whether the knobs on the ulna of Concavenator are truly quill knobs or are another feature associated with muscle attachments. For more details on this angle of the story, see the posts by Darren Naish and Mickey Mortimer.

Ortega, F., Escaso, F., & Sanz, J. (2010). A bizarre, humped Carcharodontosauria (Theropoda) from the Lower Cretaceous of Spain Nature, 467 (7312), 203-206 DOI: 10.1038/nature09181

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Stegosaurus Week: A Rare Look at Soft Tissue

The skeleton of the Hesperosaurus known as "Victoria". From Christiansen and Tschopp, 2010.

Dinosaur skin impressions are pretty rare, and, even among the known collection of these soft-tissue traces, not all dinosaurs are equally well-represented. There are plenty of skin impressions from hadrosaurs, but stegosaurs are among the dinosaurs in which the skin texture is still largely unknown. Now, as reported by paleontologists Nicolai Christiansen and Emanuel Tschopp, an exceptional specimen from northern Wyoming gives scientists a first look at the skin and other body coverings from a North America stegosaur.

The individual described by Christiansen and Tschopp, nicknamed “Victoria,” is an approximately 150-million-year-old, nearly complete skeleton of the stegosaur Hesperosaurus mjosi. Discovered in 1995, it came from the well-known Howe-Stephens quarry site, where soft tissue impressions of other Jurassic dinosaurs have been found before. Based on the state of the skeleton, it appears that the dinosaur died, was partially buried, and then completely buried by a second flow of sediment, with the best preserved elements being found on the dinosaur’s right side.

The soft-tissue impressions found in association with the skeleton were scattered around the section of the ribs just before the hips and on one of the large armor plates on the dinosaur’s back. The preservation was not complete, but rather shows bits and pieces within these areas. Even so, enough of the skin impressions were preserved to show what the skin of Hesperosaurus was like. Overall it consisted of the same kind of honeycomb scale pattern seen in hadrosaurs, horned dinosaurs and another stegosaur from Asia called Gigantspinosaurus. Rather than being uniform, however, the scale pattern differed over the dinosaur’s body, with larger, domed scales surrounded by the smaller tubercles found on skin impressions from its back.

Among the most remarkable aspects of Victoria’s remains were the soft tissue impressions from the plate. For decades paleontologists have debated what the plates would have looked like, how they were arranged, and what function they might have had, and while this new specimen probably won’t resolve the ongoing discussions about the purpose of stegosaur plates, it appears to show a relatively smooth plate covering marked by shallow grooves. That this preserved material is really from a kind of plate sheath cannot be confirmed without any doubt, but Christiansen and Tschopp make the case that this interpretation is the most consistent with the structure of the material and the existing hypothesis that stegosaur plates were probably covered in this kind of material. If further remnants of these plate sheaths can be found, they can help paleontologists better understand the anatomy of these armored dinosaurs and better test ideas about the function of their plates.

The report was published in the Swiss Journal of Geoscience as part of the proceedings from the Symposium on Stegosauria held last year. The papers cover a range of topics, from new species to the bite mechanics of Stegosaurus, and several of this week’s Dinosaur Tracking posts will feature new findings presented at the meeting. Stay tuned for more on this bizarre group of dinosaurs.

References:

Christiansen, N., & Tschopp, E. (2010). Exceptional stegosaur integument impressions from the Upper Jurassic Morrison Formation of Wyoming Swiss Journal of Geosciences DOI: 10.1007/s00015-010-0026-0

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Stegosaurus Week: The Many Postures of Kentrosaurus

The skeleton of Kentrosaurus on display at the Museum f?r Naturkunde in Berlin. From Wikipedia.

Since the early days of paleontology, the posture of dinosaurs and the range of motion they were capable of have been contentious subjects for paleontologists. During the 19th century, especially, the general view of what dinosaurs would have looked like changed no less than three times, and investigations into how these animals moved continue to this day. Among the spate of recent studies on dinosaur flexibility, posture and motion is a new paper by Heinrich Mallison which used the Jurassic stegosaur Kentrosaurus to investigate some of the hypotheses surrounding this armored dinosaur.

Most of what we know about Kentrosaurus comes from the approximately 153-million-year-old Tendaguru Formation in Tanzania. It was there that the German paleontologist Edwin Hennig found numerous isolated bones and elements of disarticulated Kentrosaurus skeletons—in addition to the bones of many other dinosaurs—during the early 20th century; he was also lucky enough to find one partial skeleton of the stegosaur that was suitable for mounting. This specimen, reconstructed with sprawling limbs and a dragging tail, was on display at the Museum f?r Naturkunde in Berlin for decades. When it was taken apart to restore it in a more accurate posture in 2005, scientists made laser scans of each bone in order to create a digital restoration. It is this digital Kentrosaurus that formed the basis of Mallison’s new study—the closest thing a paleontologist has to a living dinosaur to examine.

In addition to its normal posture and range of motion, Mallison’s study looks at several controversial, little-studied ideas about this dinosaur and its kin. According to Hennig, Kentrosaurus had a squished, lizard-like posture and could not use its spiky tail for defense. In the 1980s, however, paleontologist Robert Bakker went to the opposite extreme, restoring stegosaurs with an erect posture that would have allowed them to pivot and swing their formidable tails at attacking predators. Additionally, Bakker proposed that Stegosaurus and its kin could have adopted a “tripodal” posture in which they reared back to rest on their tails, too, and were much more dynamic animals than envisioned by Hennig and other early 20th-century paleontologists.

Although Mallison stresses that the findings based upon his model are provisional, Kentrosaurus appears to have used different postures for different reasons. While walking, it would have held its limbs erect, but when threatened it was capable of flexing its forelimbs out into a sprawling position to help support itself as it swung its tail at an offending predator. In the latter circumstance, Kentrosaurus would have also been able to extend its neck to look backwards at an attacking dinosaur, though shifting position to keep a predator in view may have created blind spots that would have left this armored dinosaur vulnerable to multiple predators. As far as feeding was concerned, Kentrosaurus was indeed capable of rearing back to rest on its tail, though how often it would have done so—and what sort of food it would have been able to reach by doing so—is unknown. Overall, Kentrosaurus was not as stiff as Hennig proposed. Quite the contrary—this stegosaur was capable of altering its posture to suit a variety of circumstances, and it is likely that at least some of its relatives had similar abilities.

References:

Mallison, H. (2010). CAD assessment of the posture and range of motion of Kentrosaurus aethiopicus Hennig 1915 Swiss Journal of Geosciences DOI: 10.1007/s00015-010-0024-2

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The Dinosaurs of Industry

A sketch of Brachiosaurus from R.S. Lull's 1920 textbook Organic Evolution.

Since the time of their discovery in the early 19th century, dinosaurs have been pop-culture superstars. Beyond their scientific identities, they have a celebrity that has remained strong from decade to decade, and given their notoriety it is no wonder that they have been so often used as metaphors and symbols.

More often than not, dinosaurs have been used as icons of stagnation. They were creatures that seemed “too big to fail”—only to have their gargantuan size turned against them. This belief stemmed from uncertainty about the extinction of the dinosaurs. At the beginning of the 20th century, many naturalists thought that dinosaurs were either out-competed by mammals or became so big and grotesque that they could no longer adapt to changing environmental conditions. Either way, they ultimately failed because they were too large and ponderous to react appropriately in the face of new challenges, and so they became the perfect icons of big business. Jay S. Miller, in a 1913 issue of the Business Philosopher, put it this way:

But why was the dinosaurs, with all its size and strength, finally compelled to succumb to its weak and apparently helpless rivals [the mammals]?

The answer is easy. It was their degree of adaptability to changed conditions.

In spite of its seeming advantages, the dinosaur possessed little ability to respond to changed conditions. Just so long as its environment was favorable and congenial it continued to flourish. But when its surroundings began to change and become less favorable it failed to adapt itself to these changes and was necessarily slowly but surely exterminated.

The lesson behind all this was that, to survive in business, being able to swiftly adapt to new conditions was key. Better to be like the small mammals than the powerful dinosaurs. A May 1919 issue of The Shoeworkers’ Journal similarly admonished cordwainers to be more like mammals and less like dinosaurs. Of dinosaurs, the article’s author, Victor McCone, said:

They planned nothing. They were contented.

They produced nothing. They were contented.

They achieved nothing. They were contented.

They voted “no” on life above the dead line.

Once again, mammals showed the potential of mental agility and innovation, leading McCone to offer his readers a choice:

Will you be a man or a dinosaur? Are you going to be chained down by beef and boneheadedness? Or will you cultivate every personal excellence, all the skill you have no matter what you are doing, and rise out of the cellar of life? It is up to you.

A century later, these disparaging perspectives of dinosaurs seem rather silly. Dinosaurs were not a homogeneous group of large, lazy, and stupid creatures that died out one by one. They were a very diverse group of organisms, one lineage of which left living descendants, and they were done-in by a cataclysmic event that wiped out a variety of organisms (including some groups of mammals). If we look back even further, we can see that the kin of the first mammals were pared back by an even worse extinction, yet it would be ludicrous to say that the origin of mammals was delayed because their ancestors were so short-sighted and slothful that they ceded ground to the more agile dinosaurs. Ultimately, any use of dinosaurs as a metaphor or symbol for human endeavor tells us more about the way we view dinosaurs than what they were actually like.

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Who Wrote the Worst Paleo-Poetry?

The skeleton of Ceratosaurus, from The Dinosaurs of North America.

I am by no means a connoisseur of poetry, but I have to admit that I can’t think of any decent poems about dinosaurs or paleontology. The poems that do exist can be almost painful to read, and, as Sarah Zielinski documented on our Surprising Science blog a few months ago, bad geological poetry has a long tradition going back to the early 19th century. Don’t just take my word for it; listed below are snippets from some dinosaur doggerel.

Edward Hitchcock – “The Sandstone Bird” (1836)

[In which the reanimated "Sandstone Bird" laments the sorry state of the modern world]

Oh how unlike Iguanodon next me
In dignity, yet moving at my nod.
The Mega-Plesi-Hylae- Saurian tribes-
Ranked next along the grand descending scale:
Testudo next below the Nautilus
The curious Ammonite and kindred forms,
All giants to the puny races here,
Scarce seen except by Ichthyosaurian eye,
Gone too the noble palms, the lofty ferns,
The Calamite, Stigmaria, Voltzia all:
And Oh! what dwarfs, unworthy of a name,
Iguanodon could scarce find here a meal!
Grow on their graves! Here, too, where ocean rolled,
Where coral groves the bright green waters graced,
Which glorious monsters made their frolic haunts,
Where strange Fucoides, strewed its very bed,
And fish of splendid forms and hues, ranged free,
A shallow brook troop, where only creatures live
Which in my day were Sauroscopic called,
Scarce visible, now creeps along the waste.

Charles H. Sternberg – “The Permian Beds of Texas” (1911)

[On an Edmontosaurus "mummy" Sternberg and his sons had found]

The glory of this specimen—
He lies there as he floated in
With bloated body on the wave.
The gas escapes he found his grave,
As he sinks to his long rest,
Skin clinging fast to bone and breast.

Samuel Ward Loper – “A Modern Dinosaur” (1911)

A startling evolution,
Onrushing through the street;
A mighty, roaring monster,
And dangerous to meet -
Like something supernatural
With fiercely blazing eyes,
And breath of vilest odor
That all around it lies

Bert Leston Taylor – “The Dinosaur” (1911)

Behold the mighty Dinosaur,
Famous in prehistoric lore,
Not only for his weight and strength
But for his intellectual length.
You will observe by these remains
The creature had two sets of brains—
One in his head (the usual place),
The other at his spinal base.
Thus he could reason a priori
As well as a posteriori.

Carl Sandburg – “The Dinosaur Bones” (1921)

The dinosaur bones are dusted every day.
The cards tell how old we guess the dinosaur bones are.
Here a head was seven feet long, horns with a hell of a ram.
Humping the humps of the Montana mountains.

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